Chlorine manufacture



Oct. 20, 19;'42. L. RosENsTr-:IN 2,299,427

CHLORINE MANUFACTURE Filed Dec. 28, 1940 Scrubber Max. Boiling HCl A`zeo+rope 2 3] ConcAqueous HClSolu'ron v Hc hcla is x Aqueous HCI Soluon Deacon Comer-rer` lnvenor Ludw ig Rosenstein atented Oct. 20, 1942 cuLonlNE MANUFACTURE Ludwig Rosenstein, San Francisco, Calif., as-

slgnor to Shell Development Company, San Francisco, Calif., a corporation of Delaware y Application December 28, 1940, Serial No. 372,094

.7 Claims.

The present invention relates to the preparaion ot freechlorine from hydrogen chloride, nd pertains more particularlytoanimproved uethod for the continuous production of chlorine y the catalytic oxidation of hydrochloric acid ras. In oneof its specific embodiments, the inrention covers a continuous process whereby high rields of chlorine may be obtained from the oxilation of hydrogen chloride, especially the hylrogen chloride which is formed as a by-product 'rom various chemical reactions, such as the rel Lotions in which chlorine is reacted, via chlorsubsttution, with saturated and/or unsaturated rganic compounds, e. g. hydrocarbons, or wheren 4chlorinated hydrocarbons are subjected to :atalytlc or non-catalytic, thermal dehydro- :hlorination to produce'unsaturated hydrocarf ons.

The reaction involving the oxidation of hyirogen chloride may be generally expressed by :he f ollowing'equation:

I'his reaction has been knownfor many years and is termed the "Deacon reaction or process. [t isalso known that removal `of the water formed as a vresult of the above oxidation of hydrogen chloride' will shift-the equilibrium to favor greater chlorine formation. Although the catalytic oxidation of hydrogen chloride accordlng tothe Deacon process may be effected by using vapors resulting from the vaporization of aqueous hydrochloric acid solutions, the resulting mixtures contain chlorine in a highly diluted state so that the recovery. of liquid chlorine therefrom is diillcult and uneconomical. On the other hand, in view of a ready market for liquid chlorine, it is highly desirable tov employ substantially anhydrous hydrogen chloride gas as the primary material in the Deacon converters so as toA decrease the water vapor content'of the effluent gases, Y A

There is a number of processes in which the resultinggaseous mixtures consist of or predominate in organic compounds, such as hydrocarbons or their chlorinated derivatives, and hydrogen chloride gas; the hydrogen chloride is normally separated from such mixtures by scrubbing with relatively large amounts of water. Therefore, the hydrogen chloride concentration in theresulting aqueous solutions is quite low. When it is desired to utilize the hydrogen chloride of such solutions asthe primary material for the production of chloliquid chlorine is to be attained, it becomes necessary to pre-treat the aqueous hydrochloric acid to obtain rst relatively concentrated solutions and even substantially anhydrous hydrogen chloride. Such pretreatment is costly and cumbersome since it necessitates the handling of relatively large volumes of dilute aqueous hydrochloric acid solutions.

It is, therefore, one of the main objects of this invention to provide a process whereby gaseous mixtures containing hydrogen chloride, as,vfor example, mixtures obtained during hightemperature chlor-substitution reactions, and/or during.

dehydrochlorination of organic chlorides, may be effectively and economically treated to recover the hydrogen chloride therefrom, and of using this hydrogen chloride as the starting material for the production of free chlorine via oxidation of such hydro'gen chloride. Another object of the invention is to afford an economical'method whereby substantially all' of the hydrogen chlo- Iride enteringthe system, or at least a predominating portion thereof, is oxidized/t produce free chlorine.

It is a further object of the present invention to provide for the utilizationf'ofall of the hydrogen chloride entering the system by effectively recovering the major portion of the hydrogen chloride which remains unreacted after the oxidation reaction,V and by `returning this hydrogen chloride substantially inan anhydrous condition and mixed with oxygen back to. the reaction chamber for the production of `further quantities of free chlorine. A still further object .of the invention is to provide an economical method for removing the excess heat of reaction I as well as the water resulting from the oxidation ofgthe hydrogen chloride, such elimination being effected substantially as soon as the water is formed, thereby favoring further chlorine formation and thel ultimate recovery of high yields thereof. Another object is to'provide a method for the continuous and economical pro- According to the usual processes,l

'.and/or dehydrochlorinatlon reactions.

duction of high yields of chlorine from hydrogen chloride gas contained in mixtures thereof with organic compounds, and particularly in gaseous mixtures resulting from the above-mentioned high temperature chlor-substitution reactions Still other objects of the invention will be` apparent and understood by reference tothe 4following portion of the specification and to the accompanying' drawing, which illustrates diagrammatically the various'essential and/or desirable rin'n'd" especially if economicalv production of 55 parts of an apparatus and their association withl each other, it being understood that details such as pumps, etc., which form no part of the invention, or which are obvious to those skilled in the art, are omitted for purposes of clarity.

It has now been discovered that the above and other objects may be attained by employingl the method described and claimed herein, the salient veyed through an oxidation reactor for the productionof further quantities of free chlorine.

' The maximum boiling azeotrope withdrawn from the aforementioned scrubber or still, after pre-- cooling to any desirable or optimum temperature,

`is-employed as the scrubbing liquid to recover v'features of which include the steps of: scrubbing a gaseous mixture comprising or consisting of hydrogen chloride from amixture thereof with saturated and/or unsaturated organic compounds, the resulting cold aqueous solution containing the absorbed hydrogen chloride being then employed to cool further quantities of the gaseous reaction mixture from the oxidizing reactor, this treatment liberating additional absorbed hydrogenv 4'chloride to be converted to chlorine.

The repeated recycling of the hydrogen chloride-chlorine mixture (together with the desired or optinium quantities lof oxygen) through the v same converter, or the consecutive passage of such tures leaving the Deacon converter or converters, this scrubbing being effected under cono, ditions whereby a maximum boiling azeotrope is obtained as -a bottomy fraction, while a gaseous 'mixture enriched by 'the hydrogen Vchloride evolved by -or released from the 'scrubbing mixture is'obtained as the overhead fraction; conveying this' gaseous mixture (if necessary with further addition of oxygen) to the same or ani; -other oxidation reactor to produce further quantities of free chlorine: andemploying the maximum-boiling azeotropes of water and hydrogen chloride (as obtained from the aforementioned v scrubbing ofrthe reaction products resulting from the above outlined oxidation of hydrogen chloride), preferably after pre-cooling,- as the scrubthe gaseous mixture entering the system.

According tofone specincembodiment of the present process, a mixture 'of hydrogen chloride and oxygen (employed in volumetric ratios de- 40. i Y

ating according to .the previously known processes.

scribed below) lis continuously conveyed through an oxidizing reactorv containing the desirable catalyst and maintained ata temperature which is conducive to the desired 'or preferred degree of conversion of the hydrogen chloride -to free chlorine'. .This temperature is generally between lmixture through a series of converters; together with the removal off the water formed after each l pass througha converter, greatly increases the conversion to chlorine, and consequently the concentration thereof lin the `eilluent gases and the overall yield of the desirable chlorine. Also, the use of the aqueous hydrochloric acid solution (i. e. the maximum boiling azeotrope) to extract` hydrogen chloride from mixtures thereof' with organic compounds., and the contacting oi' the cold liquid thus formed with the hot reaction hing liquid to recover the hydrogen chloride from products to liberate the absorbed hydrogen chloride in a substantially anhydrous state while removingthe water formed in the oxidation converter,l greatly enhances the economics ci' the process., and permits a continuous operation thereof on a commercial scale. l

Also, when the catalytic oxidation of hydrogen chloride is effected according to the process ofl the 'present'inventiom it is possible to obtain i chlorine concentrations which are considerably higher than those heretofore attainable by oper- In fact. the nal chlorine concentration of the about 385 C. and 435 C., although higherand lower temperatures may also be employedythe temperature varying".` in part with the hydrogenv chloride-oxygen ratio and, the space velocity used in the reactor. The reaction mixture leaving the reactor or converter consists of unreacted hydrogenchloride, water vapor, free chlorine and some unreacted oxygen. mixture is then conveyed continuously through-"a scrubber or still wherein the mixture is countercurrently or otherwise contacted with a cold aqueous hydrochloric acid solu-l iliuent gases is so high as to render its condensa- 'tion to liquid chlorine very simple and economi cal.

To facilitate understanding of the process of 'y the invention, reference is now made 'to the a'ccompanying drawing which illustrates. af.suit, able method for executing the saine. In thisdrawing,` numeral Il denotes a suitable chamber or converter used for effecting the Lcatalytic oxidation of hydrogen chloride, this converter 'containing any one or more of the various known oxida-` tion promoting catalysts. The composition and tion the hydrogen chloride concentrationof which is greater than that oiits maximum boiling azeotrope. Their treatment has a dual function: water vapor is condensed and removedv froml the vaporous reaction mixture in the vform ot a hydrogen chloride-water maximum boiling azeotropez simultaneously. the heat impago to the scrubbing liquid causes the evolutio the' exi cess hydrogen chloride absorbed therein so that only a maximum boiling szeotrope is withdrawn as a liquid from the bottom oi' the scrubber or still. The hydrogen chloride.y gas4 thus evolved,

v`together with the undissolved portion of the reaction mixture (i. e. the hydrogen chlolxrairtgcterI of this catalyst may vary within wide It is understood that the efficiency of 'the catay lysts. insofar astheir abilityto promote the desired oxidation ofhyd'rogen chloride is concerned. is not the same. Also, the optimumioperating 'conditionasuch as operating temperature. space velocity and theA like,-may have. to be varied depending on the specific catalyst employed. lHowever, these features are readily understandable. determinable and/or ',calculable by-a chemist skilled in the art to which the present invention (which is not directedto catalyst) pertains.

i 'The selected catalyst beingthusdisnosed inthe chamber or converter lli-,ta mixture'oi' hydrogen chloride and oxygen in the proportions hereinride. free chlorine and oxygen.'if,any) is csntinuously removed from thetop of the scrubber and, since it is substantially free from waterl vapor. may be directly and dmtmuousiyom rs.,

.after described is introduced intothis chamberthrough pipe Il, theoxygen (or an oxygen-containing gas)'being fed intov pipe", while the hydrogen chloride (which after theuse of any specific l the system through the initiation of the reaction, comes as a mixture thereof with free chlorine) is introduced into pipe II through line I3. In order to initiate the operations, hydrogen chloride may be fed into the system through line I4 provided witha valve I5.

-' The vaporous reaction products leaving the reaction chamber I0, and consisting mainly ofunre-` acted hydrogen chloride, water vapor and free chlorine, are passed via pipe I'I into a separator or still I8 wherein water is removed from the reaction vapors in the f orm of a bottom fraction comprising essentially a maximum boiling waterhydrogen chloride azeotrope. This is effected by contacting or scrubbing the vaporous reaction mixture with a cold aqueous hydrogen chloride solution the hydrogen chloride concentration of which-solution is greater than that of its maximum boiling azeotrope. This concentrated solu tio'n is fed into the separator or still I8 through pipe I9 provided with a valve 20 and leading from a source to be described below. The cold concentrated solution coming i n countercurrent contact with the hot vaporous reaction mixture eiiect's a condensation of the water vapor formed in the converter I0, this condensed water forming amaximum boiling azeotrope with a part of the V free chloride present'in still I8. Simultaneously,

the heating of the cold scrubbing solutions eil'ects a liberation of free chlorine thereof, the operating conditions in still I8 being such that the hydrogen chloride concentration of the solution leaving still I8 via line 22 is essentially that of its maximum boiling azeotrope.

The substantially anhydrous gaseous mixture withdrawn. from the upper portion' of the still I8 consists essentially of free chlorine (formedduring the oxidationreac'tion), hydrogen chlorideand some oxygen. The hydrogen chloride* in this mixture includesthe fraction which re' mained unreacted afterpassage through converter I8, and the hydrogen chloride evolved in still I8 from the cold scrubbing liquid introduced thereinto. This gaseous mixture is conveyed from is introduced through lines I2 or 21, respectively.

'The reaction mixture leaving converter 26 is enriched bythe additional quantities of chlorine formed by the catalytic oxidation of a partfof the hydrogen chloride content of the 'mixture conveyed through the reaction zone. However,

the gaseous reaction products still contain unreactedl hydrogen chloride and some 'water 60 formed as a result of the reaction. As inthe V case with the hot gaseous products withdrawn.

from reactor I0, those leaving converter 26-are conveyed via pipe 28 into the lower portionof a 56 via pipe 49.

withdrawn from the bottom via une u, and a gaseous mixture containing free chlorine and hydrogen chloride, this mixture leaving the top of the still via line 35. This gaseous mixture a' may be again repeatedly recycled- (with cooling and water removal after ach passage through a converter) until the desired chlorine concentration is attained.

' From what was said above, it isfseen that the l invention provides a. process whereby the chlorine concentration may be increased until a desired stance, as noted above, the gases from line 35 may be conveyed via valved line 36 back into converter 26 or to still another converter wherein further oxidation of the. hydrogen chloride to free chlorine may be effected. Therefore, the

invention is not limited to the use of only two oxidation reaction zones or to the recyclin through asingle converter.

When the free chlorine in the eiiluent gases leaving still 2 9 has reached a desired or optimum concentration, these gases may be treatedv to recover the free chlorine therefrom. In the specic` embodiment presented in the drawing,

this is effected by opening valve 38v and convey- 1 ing the gases via pipe 39 into. a scrubber n 40 wherein the gases are treated, for example, with water introduced via pipe 4I. The aqueous hydrochloric acid solution is withdrawn through line 42, while substantially pure chlorine is withdrawn to suitable storage via line 43. Instead of conveying all of the vapors or gases :from still 29 into chlorine separator 40, the process may be made continuous by passing a portion of the gases to this chlorine separator, while the remaining gases may be subjected to further oxidation in 4any reaction chambers of the type of converters I0, 26, o r the like. This splitting of the vaporous 40 stream maybe effected by suitable regulation or The hydrogen chloride-water maximum boiling v azeotrope withdrawn from the lower portions of stills I8 and 29 is conveyed via pipes 22 and 34 to a cooler 46 wherein the azeotrope is chilled by any of the well-knownI methods. The cold solu- 50 tion is then passed via line 41 into scrubber 48 wherein it .cornes in .contact lwith a .stream of gases containing hydrogen ,chloride (such as a gaseous mixture comprising hydrocarbons and hydrogen chloride) introduced into the scrubber The coldazeotropic solution selec.-

tively dissolves the hydrogenv chloride, so that the gases leaving the scrubber via pipe 50 are subl stantially free therefrom. If desired,'these gases (or any portion thereof) may be recycled via valved li'ne 5I so as to eiect a complete or s`ubstantially complete separation of the hydrogen chloride therefrom. The' cold solution leaving thebottom o f scrubber 48 via'line.52 thus contains a'hydrogen chlorideconcentration which is or optimum limit has been attained. For in- "still 29 wherein they are againcontacted or '55 greater than that of its'maxirnum'boiling azeo;

scrubbed with a cold Vaqueous hydrogen chloride 'ing azeotrope. l y through line 30 provided with valve 3|, and may solution the hydrogen chloride concentration of which is greater than that of its maximum boil- This solution enters still 29 or may 4not be `of the same composition'as the solution introduced into still I8 via, line. I9. The selective scrubbing or extractive distillation occurring in stili 29 produces a hydrogen chloride-water maximum boiling azeotrope which is bers, and simultaneously giving oit-the hydrogen chloride extracted from the gases in scrubber 48.

Due to the fact that water isformed as a prodr not of the hydrogen chlorideoxidation reaction"v 5 the continued operation of the above loutlined i, 'process will cause a gradual increase in the volurne of the aqueous hydrochloric acid solution. Therefore a portion of such solution may be tiall-y anhydrous condition so that itmay'- be emcontinuously or intermittently withdrawn from line 41 via pipe 55 provided with a control valve 56, and delivered to a dehydrator 51. Entering the dehydrator, which may consist ofatower containing trays, rings or other means to increase ployed as a starting material for'the production of additional quantities of free chlorine. In this connection it must be noted that the degree oi cooling of the maximum boilingaz'eotrope in cooler 46, as well as the rate of throughput of such azeotrope through scrubber d8 should be the surface extension ofthe liquid, the hydro- I This hydrogen chloride may, for example,-

aqueous sulfuric acid solution is withdrawn from the bottom of the dehydrator 51', through line 6I; This solution, if desired, may be concentrated by any of the well-known means and then/ recycled back into the'dehydrator through line 58 to remove the water from further quantities of hydrochloric acid solutions conveyed into the dehydrator 51 through line 55. Other methods oi vdehydrating the excess hydrochloric acid solution, for example, by means of calcium chloride. etc., may also be used.

'I'he above outlined process favors the cata.- lytic oxidation of hydrogen chloride to free chlorine. moval of water formed during the described oxidation reaction shifts the equilibrium of the essential reaction of the Deacon process to favor more chlorine formation. In accordance with the process oi.' .the present invention the water formed in each of thel converters is removed from the eiiiuent gases substantially as soon as formed by utilizing the azeotropic properties of aqueous hydrochloric acid. In accordance with the process-,thereaction mixture formed in the oxidation reaction is quickly conveyed to a still (e. g. still Il) and scrubbed with a cold concentrated hydrochloric acid solution to remove the waterin -the i'orm of th'e maximum boiling `-azeotrope. 'The remaining gases may then be againconveyed through the same or another converter,

regulated so as to attain proper or complete recovery of hydrogen chloride from the gaseousA mixture introduced into the system through line 49. Also, the temperature ofthe resulting concentrated hydrochloric acid solution, its hydrogen chloride concentration, as well as the ratio thereof to the hot eilluent gases in the stills, such as still i8, should be controlledrso as to eiect the desired vaporization of excess hydrogen chloride from such solution and the separation of the water formed in the converters as a maximum boiling azeotrope with hydrogen chloride. y

` Although' the .process of the present invention has been described with particular reference to the catalyticV oxidation using oxygen as the oxidizing agent, it is to be'understood that other oxygen-,containing gases, .such as air, may alsol be employed. In such'cases it is advisable to provide means forvthe continuous or intermittent separation of the inert fractions, e. g., nitrogen,

` from the reaction mixture.

This is due to the fact that the re'y Iv claim as my invention:

l. In a method of producing chlorine by the tion of hydrogen chloride to chlorine, maintaining said mixture in contact with the catalyst under oxidizing conditions for a period oi' time insufficient for the reactants and the reaction products to come tb an equilibrium, scrubbing the emuent hot gases containing -free chlorine, water vapor andunreacted hydrogen chloride with a cold concentrated aqueous hydrochloric acid solution having a, hydrogen chloride con-` centration substantially greater than that oi' its maximum boiling azeo'trope, said scrubbing solution being produced by the absorption of hydrogen chloride from a gaseous mixture of hydrogen chloride and an organic compound, its concentration, temperature and relativeamount beingsuch that the 'eiiiuent hot gas mixture is wherein further oxidation oi' the hydrogen chlo.-

ride to chlorine is effected. To readjust the com- '.position of the gas, additional iluantities of oxygen may beradded before such recycling. Operations in accordance -with the 'described -process thusprovide for an eiiicient removal of'heat and fact, 'by effecting the catalytic oxidation in a the same reaction zone and by removing the producedwater between such oxidation steps or substantially immediately after the passage of the gases through the converter, the catalytic oxildation of the hydrogen chloride to free chlorine may be carried substantially to completion,

, l Th'eprocess also provides for a continuous recovery of hydrogen chloride from gases contain'- ing' the same,- 'and the use of a cold concentrated cooled to a temperature below its dew point, such that there is produced'a vliquid fraction comprising a` water-hydrogen chloride maximum boiling azeotrope and an overhead gaseous fraction comprising a substantially anhydrous mixture of free chlorine and hydrogen' chloride, separately cool- 4 water, thereby favoring vchlorine production. In

series ot successivesteps or by recycling through solutionof such hydrogen chloride' to remove the water formed in the catalyticl oxidation cham- Y ing"`"the maximum boiling azetroper-fcontacunr" said cold, azeotrope with a gaseous mixture containing organic compounds and hydrogen chloride to form an aqueous solution having a hy.-

drogen chloride concentration greater than lthat of its maximum boiling azeotrope, using this solution as the above scrubbing solution for the hot enluent gases from the catalytic oxidation reaction zone, re-subjecting at least a portion of the substantially anhydrous overhead fraction obtained from the scrubbing oLthe eilluent gases to the above-described steps of catalytic oxidation rand scrubbing of the resultant hot eiliuent gases to maintainA a high chlorinev concentration inl v.the overhead gaseous fraction, and separating chlorine li'rom the. overhead gaseous fraction.

a substan- 75 2. A continuous process for the production o i -tained under oxidizing conditions, while scruboxidizing conditions to produce hot eilluent gases -containingfree chlorine, water vapor and unchlorine by the catalytic oxidation of hydrogen chloride which comprises establishing a plurality of reaction zones containing a catalyst which promotes the oxidation of hydrogen chloride to chlorine, conveying a gaseous mixture containing oxygen and hydrogen chloride through the rst of said reaction zones maintained under oxidizv ing conditions to produce hot eiiiuent gases con- .taining free chlorine, water vapor and unreacted hydrogenchloride, continuously scrubbing the hot eliluent gases with 'a cold concentrated hydrocomprising a water-hydrogen chloride maximum boiling azeotrope and an overhead gaseous fractionl comprising a substantially anhydrous mixture of free chlorine and hydrogen chloride, using the liquid fraction as the'labove scrubbing solution continuously and successively conveying the overhead gaseous fraction together with oxygen through the succeeding reaction zones mainchloride and oxygen through a reaction zone containing a catalyst which promotes the oxidation of hydrogen chloride to chlorine, maintaining said reactants in the reaction zone underI reacted hydrogen chloride, scrubbing the hot eiiluent gases with a cold concentrated aqueous hydrochloric acid solution having a hydrogen chloride concentration substantially greater than that of its maximum boiling azeotrope, said scrubbing solution being produced by the absorption of hydrogen chloride from a gaseous mixture of hydrogen chloridel and an organic compound, its concentration, temperature and relative amount being such that the eiiluent hot gas mixture is cooled 'to a temperature below its dew` point, such that there is produced a liquid fraction comprising a water-hydrogen chloride maximum boiling azeotrope and an overhead gaseous fraction comprising a substantially anhydrous mixture of free chlorine and hydrogen chloride, separately cooling the maximum boiling azeotrope, contacting said cold azeotrope with a gaseous mixture containing organic compounds and hydrogen chloride to lforni an aqueous solution having a hydrogen chloride concentration greater than that of its maximum boiling -azeotrope, using this solution as the above scrubbing solution for the hot efuent gases from the catalytic oxidation reaction zone, re-subjecting at least a portion of the lsubstantially anhydrous overhead fraction obtained from the scrubbing of the* 'elliuent gases to the above-described steps oi catalytic oxidation and scrubbing oi the result- 7 ant hot eiiiuent gases to maintain a high chlorine concentration in the overhead gaseous fraction,l

and separating chlorine from the overhead gaseous fraction.,

4. In al method of producing chlorine by the oxidation of hydrogen chloride, the steps oi.' conunreacted hydrogen chloride with a cold con-v veying a gaseous mixture containing hydrogen chloride and oxygen through a reaction zone containing a catalyst which promotes the oxidation of hydrogen chloride to chlorine, maintaining said mixture in contact with th'e catalyst under oxidizing conditions'ior a period of time insufflcient for the reactants and reaction products to come to an equilibrium, scrubbing the hot eiiluent gases containing free chlorine, water vapor .and

centrated aqueous'hydrochloric acid solution having a hydrogenchloride concentration substantially greater thany that of its maximum boiling azeotrope, said scrubbing solution being produced by the absorption of hydrogen chloride from a gaseous mixture of hydrogen chloride and an organic compound, its concentration, temperature and relative amount being such' that the eiiluent hot gas mixture is cooled to a temperature below its dew point, such that there is produced a liquid -bing of the hot eiiiuent vgases to maintain a high concentration of the chlorine Iin the overhead gaseous fraction, and separating chlorin the overhead gaseous fraction.

5. In a method of producing chlorine by the t oxidation of hydrogen chloride, the steps of conveying 'a gaseous mixture containing hydrogen chloride and oxygen through a'reaction zone containing a catalyst which promotes the oxidation of hydrogen chloride to chlorine, maintaining said reactants in` the reaction zone under oxidizing conditions to produce hot effluent gases containing free chlorine, water vapor and unreacted hydrogen chloride, scrubbing the hot eiliuent gases with a cold concentrated aqueous hydrochloric acid solution having a hydrogen chloride concentration substantially greater than that of its maximum boiling azeotrope said scrubbing solution being produced by the absorption of hydrogen chloride from a gaseous mixture of hydrogen chloride and an organic compound, its concentration, temperature andv relative amount being such that the eii'luent hot gas mixture is cooled to a temperature below its dew point such that there is produceda liquid fraction .comprising a water-hydrogen chloride maximum boiling prising a substantially anhydrous mixture of free vchlorine and hydrogen chloride, using the liquid fraction as the above scrubbing-solution, re-subjecting a portion oi this overhead fraction to the above-described'steps of catalytic oxidation and lscrubbing of the resultant hot eiliuent gases to maintain a. high* concentration of the chlorine in the overhead gaseous fraction,4 and recovering chlorine from the products.

6. The method according to claim 5, wherein the chlorine is recovered from the overhead gaseous fraction whichy is not 're-subjected to' the e fromv oxidation of hydrogen chloride, the steps of reacting hydrogen chloride with oxygen, at an elevated temperature andin the presence of a catalyst which-promotes the oxidation of the hydrogen chloride to chlorine, scrubbing the resulting hot eiuent gases containing free chlorine, water vapor and unreacted hydrogen chloride with a cold concentrated aqueous hydrochloric acid solution having, a hydrogen chloride concentration substantially greater than that of its maximum boiling azeotrope, said scrubbing solution being produced by the absorption of hydrogen chloride from a gaseous mixture of hydrogen chloride and.-

an organic compound, its concentration, temperature and relative amount being such that the.

eiliuent hot gas mixture is cooled to a temperature below its-dew point, such that there is produced a liquid fraction comprising a water-hydrogen chloride maximum boiling azeotropeand an overhead gaseous fraction comprising a substantially LUDWIG RosENs'rmN. 

